1. Field of the Invention
The present invention relates generally to wireless vehicle tire pressure monitoring and, more particularly, to a system and method for wireless vehicle tire pressure monitoring with improved operating efficiency.
2. Background Art
It is known in the automotive industry to provide for remote monitoring of vehicle tire parameters, particularly tire pressure. In such tire pressure monitoring systems, tire pressure sensors and radio frequency (RF) transmitters are mounted inside each tire, typically adjacent the inflation valve stem. In each tire, the tire pressure sensed by the tire pressure sensor is transmitted by the transmitter to a receiver located on-board the vehicle. The tire pressure information delivered to the receiver by the RF signals from the transmitters is subsequently conveyed to a vehicle operator or occupant, typically in the form of a display. Exemplary tire pressure monitoring systems are described and shown in U.S. Pat. Nos. 6,112,587 and 6,034,597.
The vehicle mounted receivers used in such tire pressure monitoring systems have super-regenerative topologies. It is well known that such receivers do not draw a great deal of current, and can therefore be left on or active at all times. As they are left on at all times, such receivers can detect all tire pressure information transmitted by the tire transmitters.
Such receivers, however, have low sensitivity and, in turn, lower performance. Newer receiver topologies, such as super-heterodyne, have much better performance. However, such newer receivers draw more current than receivers with older topologies. While the vehicle is on, this presents no problem and the newer receivers can be left on. However, when the vehicle is off, to meet current specifications, such receivers must be strobed on and off to keep current levels below a maximum. As a result, when the vehicle is off, it is necessary for tire transmitters to transmit a wake-up tone or signal to give the receiver time to wake-up and read the incoming tire pressure information from the tire transmitters.
The tire transmitters used in such tire pressure monitoring systems are typically battery powered. As a result, a transmitter has a limited amount of functioning time before its battery must be replaced. Transmitters typically transmit tire pressure information at short, predetermined time intervals when the vehicle is moving. To help conserve battery power, once the vehicle has been stationary for a predetermined amount of time, the transmitters transmit tire pressure information at longer predetermined time intervals.
As noted above, however, newer vehicle mounted receivers alternate between active and inactive states when the vehicle is off in order to reduce current draw. As a result, tire pressure information from tire transmitters must include a wake-up tone or signal to ensure receipt by such receivers. However, transmitting such a wake-up signal, such as in the form of a preamble or a header at the beginning of a message including tire pressure information, further shortens the limited life of a transmitter battery.
Thus, there exists a need for an improved tire pressure monitoring system and method. Such an improved system and method would include a wake-up tone or signal to ensure receipt of tire pressure information by a receiver alternating between active and inactive states. To improve operating efficiency, such a system and method would transmit such a wake-up signal only when the vehicle has been stationary for a predetermined time period, thereby facilitating conservation of transmitter battery life.